Atmel ATSTK500 500 Starter kit and development system. ATSTK500 ATSTK500 Datenbogen

 

2591C-AVR-06/06 

The communication between the STK500 and the PC is done over RS232 (PC COM 
port). The STK500 uses: 115.2kbps, 8 data bits, 1stop bits, no parity. The PC should 
be set up similarly for the communication to work. 

All commands and responses share a common message format: 

Figure 3-1. Message format. 
 

MESSAGE_START 

SEQUENCE_NUMBER 

MESSAGE_SIZE 

TOKEN 

MESSAGE_BODY 

CHECKSUM 

 

Table 3-1. Common message format fields 

MESSAGE_START 

1 byte 

Always 0x1B 

SEQUENCE_NUMBER 1 

byte 

Incremented by one for each 
message sent. Wraps to zero after 
0xFF is reached. 

MESSAGE_SIZE 

2 bytes, MSB first 

Size of the message body

(1)

 

TOKEN 

1 byte 

Always 0x0E 

MESSAGE_BODY 

MESSAGE_SIZE bytes 

Message body, from 0 to 65535 bytes

 

(1)

 

CHECKSUM 1 

byte 

Uses all characters in message 
including MESSAGE_START and 
MESSAGE_BODY. XOR of all bytes. 

Note: 

1. The current STK500 firmware can only handle messages with a message body 

of maximum of 275 bytes. 

 

The host (PC) sends commands, the STK500 responds with answers. 

One command will result in one answer. STK500 cannot send a message to the host 
that is not an answer to a received command. 

The sequence number for an answer is always the same as for the corresponding 
command. 

This section describes the state machine in the PC software that handles incoming 
packets from the STK500. When an incoming packet is expected, the state machine 
is initialized to the Start state.